第一个servlet小例子

1、sendForward.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>    
    <form action="Verify" method="post">
        请输入一个实数：<input type="text" name="number">
        <input type="submit" value="确定">
    </form>
</body>
</html>

如图所示：

2、servlet类：Verify.java

package servlet;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class Verify extends HttpServlet {

    
    public Verify() {
        super();
    }

    
    public void destroy() {
        super.destroy(); // Just puts "destroy" string in log
    }

    
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        
        response.setContentType("text/html;charset=UTF-8");
        doPost(request,response);
    }

    
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        
        response.setContentType("text/html;charset=UTF-8");
        
        String number=request.getParameter("number");
        double n=Double.parseDouble(number);    //上面是String，把String类型转为double类型
        if(n>6000||n<-6000){
            response.sendRedirect("sendForward.jsp");
        }else{
            //转发到另一个servlet文件
            request.getRequestDispatcher("ShowMessage").forward(request, response);
            
        }
    }

    
    public void init() throws ServletException {

    }

}

两种重定向方式：

（1）重定向： response.sendRedirect("sendForward.jsp");

（2）请求转发：request.getRequestDispatcher("ShowMessage").forward(request, response);

3、servlet类：ShowMessage.java

package servlet;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ShowMessage extends HttpServlet {

    
    public ShowMessage() {
        super();
    }

    public void destroy() {
        super.destroy(); 
    }

    
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        
        response.setContentType("text/html;charset=UTF-8");
        doPost(request,response);
    }

    
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out=response.getWriter();
        
        String number=request.getParameter("number");
        double n=Double.parseDouble(number);
        out.println(number+"的平方："+(n*n));
    }

    
    public void init() throws ServletException {
    }

}